Oil well perforator

ABSTRACT

This invention relates to the field of oil wells and in particular to the explosive and other devices that are used to perforate oil well casings and hydrocarbon bearing rocks in order to create channels through which oil and gas can flow into the well bore. Existing oil well perforators are either termed “big hole” perforators which are designed to produce large holes in the oil well casing only or “deep hole” perforators which are designed to perforate the casing of the well into the surrounding rocks. This invention proposes a novel “dual action” perforator capable of substantially performing the same functions as both deep hole and big hole perforators.

[0001] This invention relates to the field of oil wells and inparticular to the explosive and other devices that are used to perforateoil well casings and hydrocarbon bearing rocks in order to createchannels through which oil and gas can flow into the well bore.

[0002] The metal casing of an oil well bore is surrounded by cementwhich is in turn in contact with the hydrocarbon bearing rocks. Oil wellperforators generally perforate oil well casings in one of two ways.Deep hole perforators are designed to produce a high level ofperforation through the metal casing and cement into the hydrocarbonbearing rocks. Big hole perforators are designed to produce large holesin the casing only.

[0003] Existing perforators are deployed down the oil well casing bymounting them in a gun and hundreds may be used at any one time.

[0004] Both deep hole and big hole perforators use a form of shapedhollow charge. In its most common configuration a shaped charge consistsof a cylindrical tubular casing containing a hollow metal liner, mountedso that its axis of symmetry is coincident with that of the casing. Theliner shape is most commonly conical although other geometries such ashemispheres or trumpets can be used. The base of the liner is at the endof the cylinder facing the target and explosive is packed within thecasing and around the outside of the liner. When the explosive isdetonated at the end of the cylinder furthest from the target, adetonation front sweeps the liner causing it to collapse and produce ahigh velocity jet of liner material which is directed towards thetarget. A history of shaped charge warheads can be found in Fundamentalsof Shaped Charges by Walters W P and Zukas J A (ISBN 0-471-62172-2(1989)).

[0005] The hollow liners used in big hole perforators are generallyparabolic in shape and are made of 60Cu/40Zn brass. The apex of theliner has a hole in it which facilitates the formation of a largediameter jet (larger than if the liner surface continued all the way tothe apex). For typical pipe diameters (on the order of 100 mm), big holeperforators have a diameter of approximately 42 mm with a hole ofdiameter 10 mm in the apex of the liner. This configuration is capableof producing a hole of approximately 20-25 mm in the oil well casing.

[0006] A drawback of shaped charge based perforators is that thegeometry of the shaped charge is incapable of producing a hole greaterthan that of the diameter of the charge. Shaped charge based big holeperforators are therefore limited in the size of hole they can produce(Larger holes can be produced mechanically by milling or grinding forexample, but these processes are time consuming and costly).

[0007] The shaped charges used in deep hole perforators, in contrast tothe big hole perforators, do not have holes in the apex of the linermaterial. For these perforators a narrow, fast moving jet is required toprovide a high level of perforation through the casing, concrete andhydrocarbon bearing rock. The deep hole perforators should also be lowcost and amenable to high volume production.

[0008] It is clear that the differing geometries of the deep hole andbig hole perforator shaped charges mean that it is not usually feasibleto use a single charge to achieve both effects simultaneously. However,the highest oil and gas flows would be achieved by producing a largehole in the casing and at the same time a high level of perforationthrough the casing, concrete and hydrocarbon bearing rock.

[0009] It is therefore an object of the present invention to provide a“dual action” oil well perforator which is substantially capable ofperforming the same functions as both deep hole and big holeperforators.

[0010] Accordingly this invention provides a tandem oil well perforatorcomprising

[0011] i) a substrate,

[0012] ii) a linear cutting charge mounted upon the substrate

[0013] iii) first detonation means for detonating the cutting charge

[0014] iv) at least one hollow liner shaped charge mounted upon thesubstrate; and

[0015] v) second detonation means for detonation the hollow liner shapedcharge

[0016] wherein

[0017] vi) the substrate, cutting charge and the at least one shapedcharge are adapted for location within an oil well, and

[0018] vii) the substrate, cutting charge and the at least one shapedcharge are configured such that in use detonation of the cutting chargeby the first detonation means cuts a hole in the oil well casing anddetonation of the at least one shaped charge by the second detonationmeans causes a highly penetrating jet or jets to be projected throughthe hole in the casing.

[0019] The substrate should be any suitable means of supporting thecharges in a manner that will not interfere with their operation. Forexample, the charges could be carried on a friable substrate whichdisintegrates upon detonation of the charges. Alternatively, aconventional gun deployment system which is common in the oil and gasindustries may be used. Such gun systems would be sufficiently robust tobe withdrawn from the well bore after firing. A further alternativewould be a so-called “full flow gun system”. Such a gun system would bearranged to disintegrate upon firing in much the same way as the friablesubstrate mentioned above.

[0020] In the case of a friable substrate, the substrate should besufficiently friable such that following detonation of the cuttingcharge and shaped charge(s) it disintegrates and the debris falls downthe oil well pipe. Preferably therefore the substrate is made of a blownceramic material. Such materials are relatively light and are capable ofeasy machining thereby allowing complex shaped grooves to be created forsupport of the cutting charge/shaped charge(s). Such materials are alsosufficiently robust to be deployed down the pipe. An example of asuitable ceramic material is AL 203 manufactured by Friatec DPL inFrance.

[0021] This invention utilises explosive cutting charges to cut the oilwell casing. Such charges can be flexible linear shaped chargescomprising explosive which has been extruded together with a metal orplastic sheath (The cutting charge may be copper, silver or polymerlined). However, other versions of explosive cutting charges may berigid and pre-formed into a preferred shape or configuration. Thesecutting cords can be made into any size and can be configured into anyshape required. In use these charges chop the well bore casing intopieces that do not subsequently interfere with down hole activities.

[0022] A hollow liner shaped charge is then used to provide a high levelof perforation through the hole in the casing and into the surroundingconcrete and hydrocarbon bearing rocks. The substrate may carry one ormore of these shaped charges depending on the level of deep holepenetration required. If multiple shaped charges are used they canconveniently be formed into a focussing array for greater penetrativepower.

[0023] The use of two perforating charges in a down hole environmentenhances oil and gas flow and also enhances other activities such as thedeployment of instrumentation and sensors.

[0024] Conveniently there is a time delay between the detonation of thecutting charge and the detonation of the shaped charge(s).Traditionally, a shaped charge is detonated by detonating the explosiveat that part of the shaped charge which is furthest from the target.Therefore, a small time delay can be inserted between the firing of thefirst and second detonation means.

[0025] However, a shaped charge can be reverse initiated, i.e. thecharge can be detonated by detonating the explosive that lies at thepoints closest to the target (For the case of a conical liner this wouldequate to initiating detonation at the periphery of the base of thecone). Therefore, conveniently if the shaped charge is reverse initiatedthen the fit detonation means can also be used as the second detonationmeans.

[0026] The gape of the cutting cord (which is defined as the distanceacross the mouth of the linear charge) can be made into any sizeappropriate to the thickness of the metal to be cut. The cutting cordsshould be at a reasonably constant distance from the metal to be cut,preferably around one gape length.

[0027] Preferably the shaped charge(s) should be lined with a materialknown to be effective at penetrating concrete. Copper or preferably avery dense material such as a tungsten rich alloy should be used.However, other wrought or green compacted powder liner material, bothmetallic and non-metallic, may be equally advantageous.

[0028] Conveniently the invention can be mounted on a reusable gunarrangement similar to existing systems.

[0029] Correspondingly there is provided a method of producing holes inthe casing of oil wells and simultaneously producing perforation intothe area surrounding the oil well comprising the steps of:

[0030] i) placing an oil well perforator according to the presentinvention in an oil well at a location where it is desired to produce ahole; and

[0031] ii) detonating the oil well perforator.

[0032] In a second aspect of the invention, a dual action oil wellperforator comprises a conventional deep hole perforator and aconventional big hole perforator operating in tandem. According to thissecond aspect of the invention a tandem oil well perforator comprises

[0033] i) a substrate,

[0034] ii) a first hollow liner shaped charge mounted upon the substrate

[0035] iii) first detonation means for detonating the first hollow linershaped charge

[0036] iv) a second hollow liner shaped charge mounted upon thesubstrate; and

[0037] v) second detonation means for detonating the second hollow linershaped charge

[0038] wherein

[0039] vi) the substrate and shaped charges are adapted for locationwithin an oil well, and

[0040] vii) the substrate and shaped charges are configured such that inuse detonation of the first hollow liner shaped charge by the firstdetonation means cuts a hole in the oil well casing and detonation ofthe second hollow liner shaped charge by the second detonation meanscauses a highly penetrating jet to be projected through the hole in thecasing, the detonation of the shaped charges being sufficient todisintegrate the friable substrate.

[0041] Similar substrate configurations as described for the firstaspect of the invention above can be used in this second aspect of theinvention.

[0042] Correspondingly there is provided a method of producing holes inthe casing of oil wells and simultaneously producing perforation intothe area surrounding the oil well comprising the steps of:

[0043] iii) placing an oil well perforator according to the secondaspect of the present invention in an oil well at a location where it isdesired to produce a hole; and

[0044] iv) detonating the oil well perforator.

[0045] In this second aspect of the invention a conventional big holeperforator first cuts a hole in the oil well casing and then aconventional deep hole perforator provides a high level of perforationthrough the hole in the casing and into the surrounding concrete andhydrocarbon bearing rocks. The dimensions of typical perforator chargesmeans that this second aspect of the invention is more convenientlydeployed in larger diameter pipes of the order 12 centimetres indiameter and above.

[0046] Embodiments of the oil well perforator according to the presentinvention will now be described with reference to the accompanyingdrawings in which:

[0047]FIG. 1 shows a view of the tandem perforator and oil well in crosssection

[0048]FIG. 2 shows the oil well casing and oil well perforator incutaway

[0049]FIG. 3 shows the oil well in cross section after the perforatorhas been fired

[0050]FIG. 4 shows alternative ways of initiating detonation of theperforator

[0051]FIG. 1 shows an oil well that has been bored into hydrocarbonbearing rocks 1. The oil well comprises a metal casing 3 which issurrounded by a concrete layer 5 which separates it from the rocks 1.

[0052] The oil well perforator (7, 9, 11) comprises a friable substrate7, a cutting charge 9 and a shaped charge 11. (The detonators for thecutting charge and shaped charge are not shown).

[0053]FIG. 2 shows a 3-dimensional view of part of the metal pipe 3depicted in FIG. 1 (Note: like numerals are used to denote likefeatures). A window 13 has been cut away in the side of the pipe inorder to show the configuration of the cutting charge 9 upon thesubstrate 7. The configuration of the cutting charge 9 will be dependentupon the hole desired in the metal casing 3. In this case the cuttingcharge has been formed into an approximation of a spoked wheel. Theshaped hollow charge 11 is visible at the centre of the wheelarrangement.

[0054] Upon detonation of the cutting charge 9 by the first detonator(not shown) a hole will be cut in the metal casing 3. For theconfiguration shown a hole similar to the cutaway window 13 will beformed. After a short time delay the second detonator will detonate theshaped hollow charge 11 which will penetrate the concrete and rockbeyond the hole in the casing. Debris from the casing 3 and thesubstrate 7 will fall down the well.

[0055] The detonation of the cutting charge 9 will be a complexprocedure but it should be designed such that the cord element on theperiphery of the wheel detonates substantially simultaneously.

[0056]FIG. 3 depicts the cross sectional view of FIG. 1 after the tandemperforator has been fired. The perforator (7, 9, 11) and casingfragments have now fallen down the well and are no longer visible. Thedetonation of the shaped hollow charge has produced a deep hole 15 inthe concrete and rock.

[0057]FIG. 4 depicts various ways of initiating the perforator (7, 9,11) shown in FIGS. 1 and 2. The perforator comprises a shaped hollowcharge 11 and cutting cord 9. In a traditional mode of operation thecutting cord will first by detonated by first detonation means (notshown) at positions 20. After a short time delay the shaped hollowcharge will be initiated by the second detonator (not shown) at position22 resulting in a penetrating jet in the direction 24.

[0058] In an alternative mode of operation the first detonator also actsas the second detonator. In this case the tandem perforator is initiatedat positions 26. This results in the detonation of the cutting cordalmost simultaneously and the reverse initiation of the shaped hollowcharge. This removes the requirement to build in a time delay betweentwo separate detonators.

[0059] Other ways of configuring the cutting charge and shaped chargewill be readily apparent to the skilled person.

1. A tandem oil well perforator comprising i) a substrate, ii) a linearcutting charge mounted upon the substrate iii) first detonation meansfor detonating the cutting charge iv) at least one hollow liner shapedcharge mounted upon the substrate, and; v) second detonation means fordetonating the hollow liner shaped charge wherein vi) the substrate,cutting charge and the at least one shaped charge are adapted forlocation within an oil well, and vii) the substrate, cutting charge andthe at least one shaped charge are configured such that in usedetonation of the cutting charge by the first detonation means cuts ahole in the oil well casing and detonation of the at least one shapedcharge by the second detonation means causes a highly penetrating jet orjets to be projected through the hole in the casing.
 2. A tandem oilwell perforator as claimed in claim 1 wherein the substrate is friable.3. A tandem oil well perforator as claimed in claim 2 wherein thefriable substrate comprises a blown ceramic material.
 4. A tandem oilwell perforator as claimed in any preceding claim and further comprisingmeans for causing a small time delay between the detonation of the firstdetonation means and the detonation of the second detonation means.
 5. Atandem oil well perforator as claimed in any preceding claim wherein thefirst detonation means also acts as the second detonation means.
 6. Atandem oil well perforator as claimed in any preceding claim wherein thecutting charge is arranged in use to be at a substantially constantdistance from the casing of the oil well.
 7. A tandem oil wellperforator as claimed in claim 4 wherein the cutting charge is arrangedin use to be at a distance of approximately one gape length from thecasing.
 8. A tandem oil well perforator as claimed in any precedingclaim wherein the shaped hollow charge liner material comprises atungsten rich alloy.
 9. A method of producing holes in the casing of oilwells and simultaneously producing perforation into the area surroundingthe oil well comprising the steps of: i) placing an oil well perforatoraccording to any of claims 1 to 8 in an oil well at a location where itis desired to produce a hole; and ii) detonating the oil wellperforator.
 10. A tandem oil well perforator comprising i) a substrate,ii) a first hollow liner shaped charge mounted upon the substrate iii)first detonation means for detonating the first hollow liner shapedcharge iv) a second hollow liner shaped charge mounted upon thesubstrate; and v) second detonation means for detonating the secondhollow liner shaped charge wherein vi) the substrate and shaped chargesare adapted for location within an oil well, and vii) the substrate andshaped charges are configured such that in use detonation of the firsthollow liner shaped charge by the first detonation means cuts a hole inthe oil well casing and detonation of the second hollow liner shapedcharge by the second detonation means causes a highly penetrating jet tobe projected through the hole in the casing, the detonation of theshaped charges being sufficient to disintegrate the friable substrate.11. A tandem oil well perforator as claimed in claim 10 wherein thesubstrate is friable.
 12. A method of producing holes in the casing ofoil wells and simultaneously producing perforation into the areasurrounding the oil well comprising the steps of: i) placing an oil wellperforator according to claims 10 or 11 in an oil well at a locationwhere it is desired to produce a hole; and ii) detonating the oil wellperforator.